Melting, refining and preparation for casting of magnesium and like metals



April 20, 1937. L G. DAY 2,077,990 MELTING, REFINI'NG AND PREPARATION FOR CASTING 0F MAGNESIUM AND LIKE METALS Filed May 29; 19:56 1 2 Sh'eets-Sheet 1- April 20, 1937. L & DAY 2,077,990 MELTING, REFINING AND PREPARATION FOR CASTING OF MAGNESIUM'AND L IKE METALS Filed am 29; 1936 2 Sheets-Sheet 2 //v we a!" atented Apr. 2%, E3

MELTENG, an son cas'rmc LIKE METALS a rnarnaa'rrou or MAGNESIUM arm Leslie George Day, Taplow, England, assignor to Magnesium Castings and Products Limited, Slough, England and to High Duty Alloys- Limited, Slough, England Application May 29, 1936, Serial No. 82,644 In Great Britain rum 1, 1935 9 Claims.

The present invention relates to the melting,

refining and preparation for casting of metals such as magnesium or magnesium alloys which in the molten form are subject to attack in the covered with a layer of protective flux. The

use of suchaflux has several serious disadvantages. .the chief of which is that particular care must be exercised in pouring or otherwise removingvthe 20 metal from beneath the flux withoutentraining the flux with the molten metal, and even with meticulous care there is a likelihood of a certain proportion of flux being entrained.

It has been proposed to use inert gases for protecting the surface of the-molten metal, but when working with a stock of such metal from which portions are withdrawn with the aid of a ladle eddying of the gases occurs at the aperture through which the. ladle is inserted and 30 consequently air enters the furnace and attacks the surface of the metal- Moreover, the inert gases which may be,used,- for example sulphur dioxide, are usually of such nature that any substantial concentration thereof is injurious to 5 the operatives and consequently it is not feasible to prevent the entry of air into the furnace .by supplying a rapid stream of the inert gas to within the furnace. or completely effective use of an inert gas a totally enclosed container might be used in certain circumstances, but it-is oi viously impracticable in melting and ladlin operations-of the kind described.

. The present invention consists in a method of melting, refining and preparing for casting of metal such as magnesium in a furnace having an aperture above the surface of the metal of size suilicient to admit a ladle, according to w ch an inert gas is slowly introduced into or enerated within the furnace, either continuously 50 or intermittently, above the surface of the metal and .a g I aperture and in a plane substantially parallel to the plane of the said aperture, the extent and the velocityof the gas flow being sumcient to prevent 55 the entrance of air through the aperture.

flow is established adiacent to the In carrying out the present invention it is preferred to establish the gas flow by means of a number of jets of combustible gas. e. g. ordinary coal gas, which burn and are suitably directed in the neighbourhood of the aperture. When estab- 5 lishing the gas flow of this nature it is furthermorepreferred to conduct the whole operation under a suitable hood so that the hot products of combustion may be withdrawn to a stack. The draught thus induced facilitates the establish- 10 ment of a satisfactory gas flow. The combustible gas may for example be "supplied from two series of jets located laterally of the aperture and directed inwardly and from another series of jets located beneath the aperture and directed upwardly, the jets in both series lying in a plane parallel to the plane of the aperture. The stream of hot combustion gas thus generated not only serves to prevent any currents of air from entering the furnace, but also serves to carry off the slow stream of inert gas which is supplied within the furnace and which leaks outwardly through the aperture. Thus, when the whole operation is conducted under a suitable hood and the hot products of combustion withdrawn to astack it is possible to use as the inert gas supplied within the furnace a'rela tively noxious gas such as sulphur dioxide without harmful effect on the operatives. Other inert gases may be admitted, however, within the' 0 furnace such for example as carbon monoxide, carbon dioxide or the products of combustion for example of ordinary coal gas.

One way of carrying the invention into effect will now be described with reference to the ac companying diagrammatic drawings, wherein:

Figure 1 represents a front elevation of a. furnace, and r I Figure 2 is a sectional elevation through the centre ofFlaure 1.

Referring-to the drawings:-

A circular oil or gas -fired melting furnacel contains a suitablyshaped melting pot? covered by 'a dome-shaped cover 3 which is jointed by flanges and an'asbestos ring 4 to thepot 2.

A vertical aperture 5 of a size which will permit of the introduction of the ladle is formed in the cover 3, which latter is also provided with several small holes 6 through which asupply of sulphur dioxide may be introduced into the space I above the molten metal 8 by way of the pipe 9. The positioning of these inlet holes 6 should be such that the inert gases let in above the metal should come in at as many points as possible and be so distributed that'the gas readily covers the whole surface of the metal.

In the particular example under consideration two of these inlet holes are placed close to the 5 aperture. A gas burner in the form of two vertical arms III, II rising from a horizontal portion I I2 is placed immediately in front of the ladling aperture 5 so as to frame the aperture on three sides.

The plane of the-burner is substantially parallel to the plane of the mouth of the ladling aperture and the three parts of the burner are perforated along their inner sides in such a manner as to tend to throw jets of burning gas across the aperture in the plane of the burner. Situated vertically above the burner and aperture is a 'hood I3 and stack pipe l4 arranged in such a manner that the hot gases from the burner together with excess protective gases'are collected by the hood and forced up the stack pipe.

Sliding doors. IS, IS normally close'the aperture 5 but are moved aside when a ladle is'to be introduced for the removal of metal for casting. In carrying out the melting operation in the above described apparatus, the crucible 2 is charged with a suitable quantity of magnesium and heavy density flux.

As soon as the melting commences the part of the pot above the molten metal is-fllled with sul- .phur dioxide and the gas ignited on the burner ill, Ii, 12 in front of the aperture. A slow stream of sulphur dioxide intd'the' pot is then main-.' tained during the whole of the succeeding opera-.

tions. The metal when molten is stirred up with .35 the flux which sinks to the bottom and the metal may then be'raised to temperatures considerably above those usual in casting without the slightest. trace of the burning or sparking which is usual on the surface of molten magnesium. The

40 gas burner, hood and stack pipe prevent air from being carried on to the surface of the molten magnesium and at the same time leaves the metal freely accessible for stirring;'skimming, ladling or other operations connected with its operation for casting.

' General Inert gasesother thansulphur dioxide, for

instance, carbon dioxide, carbon monoxide, or the rare gases argon, helium, neon, krypton, xenon 5 may be used for filling the space above the molten.

metal and means other than the gas jets described above may be used for producing the desired sealing gas stream:-

i The process described above is of particular advantagein those cases where a large charge of metal is kept at the optimum temperature for casting and has to be distributed among a number of moulds, since by this process: each casting may be made with metal of the same temperature.

The aperture should be of such size as to permit of the free use of a suitable ladle and may therefore be ultilized for-inspection or manipulation of the charge for example stirring under 65 visual control, or for charging and recharging the furnace during the melting operation.

Having now described my invention, 'what I claim as new and desire to secure by Letters Patent is:- A

1. A process for the melting, refining and preparation for casting of light metals such as magnesium or magnesium alloys, which are vigorously attacked by air when molten, which consists in melting the metal in a covered crucible having an aperture above the surface of the metal in a substantially vertical plane and of a size sumcient to admit a casting ladle, maintaining an atmosphere of inert gas above the surface of the' metal at a pressure slightly above that of the atmosphere and passing an independent sealing gas stream-adjacent to and substantially parallel to the plane of the face of the said aperture on the outer side thereof.

2. A process as claimed in claim 1 wherein the inert gas atmosphere is maintained by slowly passing inert gas into the space above .the surface of the metal.

3. A- process as claimed in claim 1 wherein the inert gas atmosphere ismaintained by generating inert gas in the space'above the surface of the metal.

inert gas is sulphur dioxide.

8. Apparatus for melting, refining and preparing for casting metals such as magnesium including a covered crucible having an aperture of considerable size and ina substantially vertical plane above the molten metal level, means for covering the molten metal with an inert gas at a pressure slightly abovethat of the atmosphere and meansfor producing an independent stream of gas adjacent to and across the aperture so as to prevent the passage of atmospheric air therethrough.

9. Apparatus as claimed in claim 8 wherein the aperture in. the upper part of the crucible is normally closed by suitabledoors, the means for covand the means for producing the stream of gas comprises a burner arrangedclose to and around the sides and bottom of the aperture so as to project jets of-burning-gas in a plane close to'and substantially parallel to the plane of the orifice and a hood and stack pipe arranged above the burner to carry off the products of combustion and any excess inert gas from the interior of the crucible.

LESLIE GEORGE DAY.

-ering the surface of the metal with inert 8&5 comprises a series of inwardly directed nozzles arranged around the circumference of the crucible 

